GCSE AQA Chemistry C1

What is an element?

A substance made of only one type of atom

What is a compound?

A substance containing two or more different elements chemically combined in fixed proportions

What is a mixture?

Two or more elements or compounds not chemically combined together

How can mixtures be separated?

By physical processes that do not involve chemical reactions

What is filtration used for?

To separate an insoluble solid from a liquid

What is crystallisation used for?

To separate a soluble solid from a solvent

What is simple distillation used for?

To separate a liquid from a solution based on boiling point

What is fractional distillation used for?

To separate a mixture of liquids with different boiling points

What is chromatography used for?

To separate mixtures of soluble substances based on their relative solubilities

What is the stationary phase in paper chromatography?

The chromatography paper

What is the mobile phase in paper chromatography?

The solvent

Why must the baseline be drawn in pencil in paper chromatography?

Pencil is insoluble in the solvent so it will not run or contaminate the results

State the equation to calculate the Rf value in chromatography?

Rf = Distance moved by spot / Distance moved by solvent front

What was John Dalton's model of the atom?

Tiny spheres that could not be divided

What subatomic particle did JJ Thomson discover?

The electron

What was JJ Thomson's model of the atom called?

The plum pudding model

Describe the plum pudding model of the atom

A ball of positive charge with negative electrons embedded in it

What experiment disproved the plum pudding model?

The alpha particle scattering experiment

What was observed during the alpha particle scattering experiment?

Most alpha particles passed straight through, but a small number were deflected or bounced back

What conclusion was drawn from most alpha particles passing straight through the gold foil?

Most of the atom is empty space

What conclusion was drawn from alpha particles being deflected in Rutherford's experiment?

The mass and positive charge of the atom are concentrated in a central nucleus

How did Niels Bohr adapt the nuclear model of the atom?

He suggested that electrons orbit the nucleus at specific distances in energy levels (shells)

Which subatomic particle did James Chadwick discover?

The neutron

What particle was discovered that accounts for the positive charge of the nucleus?

The proton

What are the three subatomic particles in an atom?

Protons, neutrons and electrons

What is the relative electrical charge of a proton?

+1

What is the relative electrical charge of a neutron?

0

What is the relative electrical charge of an electron?

-1

What is the relative mass of a proton?

1

What is the relative mass of a neutron?

1

What is the relative mass of an electron?

Very small (1/2000)

Why do atoms have no overall electrical charge?

The number of positive protons equals the number of negative electrons

What does the atomic number of an element tell you?

The number of protons in an atom

What does the mass number of an element tell you?

The total number of protons and neutrons in the nucleus

State the equation to calculate the number of neutrons in an atom

Number of neutrons = Mass number - Atomic number

What is the approximate radius of an atom?

1 x 10^-10 metres (0.1 nanometres)

What is the approximate size of a nucleus relative to the whole atom?

Less than 1/10,000th of the radius of the atom

Where is almost all the mass of an atom concentrated?

In the nucleus

What is an isotope?

Atoms of the same element with the same number of protons but different numbers of neutrons

What is relative atomic mass (Ar)?

The weighted average mass of atoms of an element compared to 1/12th the mass of a carbon-12 atom

State the formula to calculate relative atomic mass from isotopic abundances

Ar = sum of (isotope mass x isotope abundance) / sum of abundances

How many electrons can the first energy level (shell) hold?

Up to 2

How many electrons can the second energy level (shell) hold?

Up to 8

How many electrons can the third energy level (shell) hold?

Up to 8

How are elements arranged in the modern periodic table?

In order of increasing atomic number

What do elements in the same group of the periodic table have in common?

They have the same number of electrons in their outer shell and similar chemical properties

What does the period number in the periodic table represent?

The number of energy levels (shells) an atom has

How did John Newlands arrange the elements in his periodic table?

In order of atomic weight, developing the Law of Octaves

Why was Newlands' Law of Octaves rejected by other scientists?

He grouped elements together that had completely different properties and broke the pattern

How did Dmitri Mendeleev overcome problems with ordering elements by atomic weight?

He left gaps for undiscovered elements and changed the order of some elements to fit properties

Why was Mendeleev's periodic table accepted by the scientific community?

Missing elements were discovered and their properties matched his predictions closely

Why did ordering elements by atomic weight cause errors before the discovery of isotopes?

Isotopes exist, meaning atomic weight is an average and does not strictly increase in order of atomic number

What type of ions do metals form when they react?

Positive ions

What type of ions do non-metals form when they react?

Negative ions (or they share electrons)

Where are metals found on the periodic table?

On the left and towards the bottom

Where are non-metals found on the periodic table?

On the right and towards the top

State three physical properties typical of metals

High melting/boiling points, good conductors of electricity/heat, and malleable

State three physical properties typical of non-metals

Low melting/boiling points, poor conductors of electricity/heat, and dull/brittle

What are Group 0 elements known as?

The noble gases

Why are Group 0 elements extremely unreactive?

They have a full outer energy level of electrons, making them stable

What is the trend in boiling points down Group 0?

Boiling points increase down the group

Why do boiling points increase down Group 0?

Relative atomic mass increases, leading to stronger intermolecular forces requiring more energy to overcome

What are Group 1 elements known as?

The alkali metals

How many electrons do Group 1 elements have in their outer shell?

One

What is formed when a Group 1 metal reacts with water?

A metal hydroxide and hydrogen gas

What is the word equation for sodium reacting with water?

Sodium + water -> sodium hydroxide + hydrogen

What is observed when potassium reacts with water?

It fizzes rapidly, melts into a ball, and burns with a lilac flame

What is formed when a Group 1 metal reacts with oxygen?

A metal oxide

What is formed when a Group 1 metal reacts with chlorine?

A white metal chloride salt

What is the trend in reactivity down Group 1?

Reactivity increases down the group

Why does reactivity increase down Group 1?

The outer electron is further from the nucleus, shielding increases, electrostatic attraction weakens, so the outer electron is lost more easily

What are Group 7 elements known as?

The halogens

What form do elemental halogens exist in naturally?

Diatomic molecules (pairs of covalent atoms)

What is the trend in reactivity down Group 7?

Reactivity decreases down the group

Why does reactivity decrease down Group 7?

The outer shell is further from the nucleus, shielding increases, attraction weakens, so an electron is gained less easily

What is the trend in melting and boiling points down Group 7?

Melting and boiling points increase down the group

What is a halogen displacement reaction?

A more reactive halogen will displace a less reactive halogen from an aqueous solution of its salt

Give the word equation for chlorine reacting with potassium bromide

Chlorine + potassium bromide -> potassium chloride + bromine

Where are the transition metals located on the periodic table?

In the central block between Group 2 and Group 3

Compare the melting points of transition metals to Group 1 metals

Transition metals have much higher melting points

Compare the density of transition metals to Group 1 metals

Transition metals are much denser and harder

Compare the reactivity of transition metals to Group 1 metals

Transition metals are much less reactive with water, oxygen and halogens

What is a key chemical property of transition metals regarding ions?

They can form ions with different charges (variable oxidation states)

What type of compounds do transition metals form?

Coloured compounds

What is an important industrial application of transition metals and their compounds?

They are used as catalysts in chemical reactions

Name a transition metal used as a catalyst in industry

Iron (used in the Haber process)